Valve actuator for actuating a gas exchange valve of an internal combustion engine

ABSTRACT

A valve actuator for operating a gas exchange valve of an internal combustion engine has a sleeve-shaped positioning piston which is connected to a valve stem, has at least two shell-shaped wedge pieces enclosing a stem end of the valve stem, whose radially outer peripheral surfaces have a conical segment which tapers off with increasing distance from the gas exchange valve and which is at least partially surrounded by a conical clamping sleeve having a mating conical inner surface and is connected to the positioning piston. The wedge pieces are axially form-fittingly and rotatably connected to a threaded bolt. A threaded segment is provided on the threaded bolt via which the wedge pieces and the conical clamping sleeve are axially attachable to one another.

BACKGROUND INFORMATION

German Patent Application No. DE 10 116 218 describes a valve actuator,in which one stem end of the gas exchange valve is connected to apositioning piston of the valve actuator via at least two shell-shapedwedge pieces which enclose the stem end and are axially supported by thepositioning piston, the radially outer peripheral surface of the wedgepieces having a conical shape and being enclosed by a conical clampingsleeve. The conical clamping sleeve has a radially inner peripheralsurface, whose shape is complementary to the conical angle of the wedgepieces and which is axially clamped against the wedge pieces by athreaded connection formed on the wedge pieces. Due to the conical angleand thread on the wedge pieces, these are relatively complex components,which are very costly to manufacture.

SUMMARY OF THE INVENTION

According to the present invention, a threaded bolt, axiallyform-fittingly and rotatably connected to the wedge pieces, is providedfor connecting the gas exchange valve to the valve actuator. Themanufacturing complexity is considerably reduced due to the provision ofthe conical angle and threaded connection functions on separatecomponents.

According to a preferred embodiment, the wedge pieces may extend beyondthe stem end as an axial extension of the valve actuator, beingconnected there to the threaded bolt. The wedge pieces then conicallytaper off with increasing distance from the gas exchange valve and areattached to the conical clamping sleeve via the thread formed on thethreaded bolt.

The number of valve actuator components may be reduced due to the factthat the conical clamping sleeve is formed in one piece by thepositioning piston and the threaded segment engages with a matingthreaded segment on a radially inner peripheral surface of thepositioning piston.

The threaded bolt may be connected to the wedge pieces in a particularlysimple manner via annular bulges, peripherally situated on the wedgepieces and the threaded bolt, which engage in annular grooves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lateral cross section of a preferred embodiment of avalve actuator according to the present invention.

FIG. 2 shows a cross section along line II-II in FIG. 1.

FIG. 3 shows a cross section along line III-III in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a gas exchange valve 1 of a valve drive of an internalcombustion engine, the gas exchange valve being operated by apositioning piston 2 of a valve actuator 4 in such a way that itperforms upward and downward opening and closing movements in the axialdirection.

Gas exchange valve 1 has, as is known, a valve stem 5, which extends inthe axial direction away from the combustion chamber of the internalcombustion engine. Valve stem 5 has a stem end 5 a, distal from thecombustion chamber, which is surrounded by two half-shell-shaped wedgepieces 6, 7. Stem end 5 a has at least one annular groove 8, into whichat least one annular bulge 9 formed on the inner periphery of wedgepieces 6, 7 engages radially. In the present example, a total of threeaxially equidistant annular grooves 8 on valve stem 5 and three matingannular bulges 9 are provided. Annular bulges 9 are formed byessentially semicircular partial bulges on both wedge pieces 6, 7 whichcircularly complement one another, forming annular bulges 9.

Wedge pieces 6, 7 form on their outer peripheral surface a conicallyshaped segment 10, which tapers off with increasing distance from gasexchange valve 1. The two wedge pieces 6, 7 together form a clampingwedge 11, which cooperates with a mating conical inner surface 12 of aconical clamping sleeve 13. Conical clamping sleeve 13 is formed on anend 14 of positioning piston 2 proximal to the combustion chamber in onepiece with the positioning piston.

Positioning piston 2 extends in the axial direction along an axis 15concentrically to a longitudinal axis 17 of valve stem 5 of gas exchangevalve 1. Valve actuator 4 has an actuator housing 20, which is axiallytraversed by positioning piston 2. A guide sleeve 18, within whichpositioning piston 2 is guided in its axial displacement via a guidecollar 23 on positioning piston 2, is located in actuator housing 20. Afirst chamber 22, which is connected to a first pressure medium line(not illustrated in detail) via a first opening 21 in the wall ofactuator housing 20, is formed in actuator housing 20 on the side ofguide collar 23 facing the combustion chamber. First chamber 22 isdelimited by actuator housing 20, guide sleeve 18 and positioning piston2, including guide collar 23. A first sealing ring 26 prevents thepressure medium in first chamber 22, for example, hydraulic fluid, fromescaping from actuator housing 20 via a first annular gap 24.

A second chamber 25, which is connected to a second pressure medium line(also not illustrated in detail) via a second opening 27 in the wall ofactuator housing 20, is formed in actuator housing 20 on the side ofguide collar 23 facing away from the combustion chamber. Second chamber25 is also delimited by actuator housing 20, guide sleeve 18 andpositioning piston 2, including guide collar 23. A second sealing ring28 prevents the pressure medium in second chamber 25 from escaping fromactuator housing 20 via a second annular gap 29.

Positioning piston 2 is designed in the form of a hollow cylinder. Aconstriction 38 on the inner periphery of positioning piston 2 islocated between conical sleeve 13 proximal to the combustion chamber andan end 2 a of positioning piston 2 distal from the combustion chamber.An inner thread 39 is formed in the area of constriction 38, whichengages with a mating outer thread 40 on a threaded bolt 41. Threadedbolt 41 is situated concentrically within positioning piston 2. Outerthread 40 extends via a threaded segment 31 axially to threaded bolt 41and engages, at least partially, with outer thread 40.

Threaded bolt 41 is axially connected to valve stem 5 in a form-fittingmanner so it is able to rotate in the peripheral direction. For thispurpose, conical clamping sleeve 13 and wedge pieces 6, 7 extend beyondstem end 5 a of valve stem 5, surrounding end 41 a of threaded bolt 41proximal to the combustion chamber. At least one radial projection 42,which in the present example is designed as an annular bulge engagingradially in at least one depression 43 on the outer periphery ofthreaded bolt 41, is provided in the area of end 41 a on the innerperiphery of clamping wedge 11. Depression 43 is designed in the presentexample as an annular groove and there are a total of three axiallyequidistant bulges 42 situated on clamping wedge 11 and three matinggrooves 43 on threaded bolt 41 which radially engage with bulges 42.

As is apparent from FIG. 2, an end 41 b of threaded bolt 41 distal fromthe combustion chamber is designed as an outer hexagon 45 for theapplication of a wrench (not illustrated). Threaded bolt 41 may bescrewed into inner thread 39 using the wrench, clamping wedge 11 beingaxially and radially clamped to conical clamping sleeve 13 due to theform-fitting connection to clamping wedge 11. To prevent positioningpiston 2 from being entrained by friction into rotation when threadedbolt 41 is screwed in, a second, also hexagonal, wrench may be used in atool receptacle 46 on stem end 2 a to secure it.

FIG. 3 also shows that both wedge pieces 6, 7 rest radially in the shapeof a half-shell on the conical clamping sleeve.

Against this background, the function of the valve actuator is thefollowing:

FIG. 1 shows gas exchange valve 1 in an open position, in which bothchambers 22, 25 are pressurized via the pressure medium lines. Due tothe smaller axial piston surface area of positioning piston 2 on firstchamber 22, positioning piston 2 is axially offset with respect to thecombustion chamber. Second chamber 25 is depressurized to close gasexchange valve 1; first chamber 22 always remains pressurized. Due tothe overpressure in first chamber 22, positioning piston 2 is then movedupward toward second chamber 25.

To assemble valve actuator 4, gas exchange valve 1 is introduced intothe valve stem guide of the cylinder head (not illustrated) and thenwedge pieces 6, 7 are placed on stem end 5 a. End 41 a of threaded bolt41 is also secured between wedge pieces 6, 7. Subsequently, valveactuator 4 is placed from above onto the pre-assembled components gasexchange valve 1, threaded bolt 41, and wedge pieces 6, 7 until theouter surface of clamping wedge 11 comes to rest on conical innersurface 12. A wrench is then positioned in positioning piston 2 on outerhex 45, and threaded bolt 41 is axially adjusted by rotating over thread37, 39. In this way, clamping wedge 11 and conical clamping sleeve 13are attached to each other. Positioning piston 2 may have to be securedin the direction of rotation using another tool.

The applicability of the present invention is not limited to theabove-described exemplary embodiment. Thus, numerous modificationoptions of the specific embodiment are conceivable, which do notessentially alter the inventive idea. Thus, positioning piston 2 may beinstalled more or less completely in actuator housing 20. The number ofgrooves 9, 43 and bulges 8, 42 may vary. The grooves and bulges may alsobe formed on another component without modifying the operating principleof the valve actuator. The points of application of the wrenches may bedesigned differently from the above-described embodiment.

1-8. (canceled)
 9. A valve actuator for operating a gas exchange valveof an internal combustion engine, comprising: a valve stem; a conicalclamping sleeve; a sleeve-shaped positioning piston connected to thevalve stem; at least two shell-shaped wedge pieces, which enclose a stemend of the valve stem, and whose radially outer peripheral surfaces havea conical segment which tapers off with increasing distance from the gasexchange valve and which is at least partially surrounded by the conicalclamping sleeve having a mating conical inner surface and is connectedto the positioning piston; and a threaded bolt, the wedge pieces beingaxially form-fittingly and rotatably connected to the threaded bolt, thethreaded bolt having at least one threaded segment via which the wedgepieces and the conical clamping sleeve are axially attachable to oneanother.
 10. The valve actuator according to claim 9, wherein the wedgepieces extend beyond the stem end as an axial extension of the valvestem and there partially encompass the threaded bolt axially in aform-fitting manner.
 11. The valve actuator according to claim 9,wherein the conical clamping sleeve is formed by the positioning piston,and the threaded segment at least partially engages with a mating threadon the positioning piston.
 12. The valve actuator according to claim 11,wherein the threaded segment extends in an axial direction on an outerperiphery of the threaded bolt.
 13. The valve actuator according toclaim 12, wherein at least one radial projection, which radially engageswith at least one radial depression on an inner surface of the wedgepieces, is formed on the outer periphery of the threaded bolt.
 14. Thevalve actuator according to claim 13, wherein the at least one radialdepression and the at least one radial projection have an annular shape.15. The valve actuator according to claim 14, wherein the at least onedepression on the threaded bolt is situated in an area of its end facingthe valve stem, and the threaded segment is behind the stem end, viewedin an axial direction from the gas exchange valve.
 16. The valveactuator according to claim 15, wherein three peripheral depressions aresituated on the threaded bolt which each engage with three matingprojections on the wedge pieces.